It is known in the art to which the present invention pertains, to provide devices which deliver a fluid medicament from a drug bag to a line leading to an infusing needle or catheter. Many such devices utilize mechanical pumping means for delivering the fluid i.e. peristaltic pumps, etc. As well, it is known in the art to provide means for controlling the rate at which the fluid is delivered.
For example, Australian Patent Application No. 61546/86 to Cannon et al. published May 28, 1987 teaches an infusion device which includes a peristaltic pump that is used in association with a strain gauge assembly which monitors dimensional changes in the outer diameter of an I.V. tube. The fluid flow through the infusion tube is motivated by the pump which, through a series of fingers which massage the I.V. tube, cause the fluid flow. The rate of fluid delivery is determined from a reading from the strain gauge. From this determination, a controller operates the pump to vary the rate of flow, if necessary. There are disadvantages to the use of mechanical means such as peristaltic pumps to deliver fluids, including the costs associated with such fluid pumps which include the costs of maintaining the pump. Further, the fluid to be delivered is gravity fed from a reservoir thereby interfering with the portability of the system.
Other references which include direct displacement pumping means include U.S. Pat. Nos. 4,670,006 to Sinnett et al. and 4,998,914 to Wiest et al.
U.S. Pat. No. 4,670,006 teaches an infusion device which includes an electrically driven fluid pump combined with a pressure regulator and pressure detecting means, as well as a motor control unit for the pump. The device monitors the fluid delivery pressure and activates the fluid pump when the pressure falls below a predetermined level. As already stated above, the use of a pump assembly for pumping a fluid directly provides certain disadvantages in both costs and maintenance. Further, the configuration of detection and control means is not practical for use in a portable infusion unit.
U.S. Pat. No. 4,998,914 describes a perfusion system which uses a perfusion pump connected with a perfusion line having a pressure sensor for determining the flow rate of fluid to be delivered. This device also provides for gravity feeding of the perfusion fluid to the pump. The perfusion system monitors the pressure within the body cavity being perfused. This is useful in such a perfusion system, but not necessary for use in an infusion system. Again, the cost and maintenance of the fluid pump poses certain disadvantages, as does the gravity feed of the pump.
PCT application WO 90/07942 to Wojcicki et al. purports to teach a fluid delivery system which includes a volumetric pump and a method of continuously monitoring the operation of the delivery system for controlling the pump. The control method of this reference is characterised by the measurement of actual pressure of delivery of a fluid with every cycle of the volumetric pump. Such measurement requires certain electronic sensing and calculation means which add to the cost and complexity of the infusion system. Again, as stated above, volumetric pumps have disadvantages relating to both cost and maintenance.
European patent application 277,518 to Heitmeier et al. discloses a pressure infusion device, again in which an infusion pump is used to control the rate of flow of the infused liquid. The infusion pump is operated by a control circuit which measures the rate of flow of infused liquid between two sensors which are separated along the infusion tube. The volume of flow is calculated and the controller adjusts the speed of the pump, if necessary. Gravity feed is used to supply the pump thereby reducing the portability of the system. Again, the use of an infusion pump will add to the cost and maintenance disadvantages of the system, as will the electronics required to control the infusion pump on the basis of measurements made between the two sensors. The gravity feed will limit the portability of the system.
It is also known in the art to which the present invention pertains, to provide infusion devices which transfer a fluid medicament from a drug bag or reservoir using means to pressurize the drug bag or reservoir. The pressurizing means is useful in combination with a flow regulator which is part of the delivery line.
U.S. Pat. No. 4,267,834 to Barger et al. discloses a device for flushing a medical fluid through an infusion line used for monitoring blood pressure fluctuations. The rate at which the fluid is infused to the patient is controlled in part through a compression sleeve connected to a pressure gauge and adjustable using a squeeze bulb. Although simple to operate, the flowrate of fluid through the infusion tube is not precisely controlled as the pressure to the drug bag must be monitored and adjusted manually. Such an infusion system would not be practical for the infusing of a drug at a constant flow rate.
U.S. Pat. No. 5,059,182 to the present inventor, describes a portable infusion device which includes an inflatable bag carried in a container within which a drug bag filled with a fluid to be infused is placed. The pressure imparted by the inflatable bag to the drug bag motivates the fluid therein to flow through a tube to the patient to which the fluid is being delivered. Flow rate control is achieved through the use of a flow regulator in combination with the monitoring the pressure imparted by the inflatable bag on the drug bag. Again, the flow rate control of infused fluid is not easily maintained as constant monitoring and manual adjustment of the pressure of the inflatable bag is necessary.
U.S. Pat. No. 4,505,264 to Parmelee et al. describes a portable infusion device in which a drug bag containing a fluid to be infused is placed within a rigid container having a spring biased plate to impart a pressure on the drug bag to motivate the fluid to flow into the connecting tube. The flow rate is controlled by regulators connected in series with the tube. The use of the spring biased plate results in a variable pressure imparted to the drug bag as the drug bag drains (i.e. over the range of movement of the spring biased plate). As a result, higher flow rates will be experienced initially, compared to lower flow rates which will be experienced when the drug bag nears depletion. This variable flow rate is unacceptable in a fluid infusing device.
U.S. Pat. No. 4,557,726 to Reinicke describes a medication dispensing system in which a medication to be infused fills a reservoir over which a constant pressure is maintained through the use of a fluid which has two-phases (gas and liquid) body temperature. The flow through the infusion tube is controlled by means of a regulator. The pressure of the fluid infusate is not utilized or adjusted to maintain a constant flow rate of infusate to the patient.
Similarly, Canadian Patent No. 1,152,823 to Dorman and Canadian Patent No. 2,021,284 to Sampson both also utilize regulator devices in series with an infusate line maintained at a constant pressure for controlling the flow infusate to the patient. Neither reference discloses a manner of measuring and thereby controlling the pressure of infusate to regulate the flow to the patient.
U.S. Pat. No. 4,077,405 to Haerten et al. discloses an apparatus for infusing liquids wherein a supply reservoir of the infusate liquid is maintained at a pressure in excess of the pressure prevailing at the point of liquid discharge to the patient. Preselectable constant volumes of liquid are discharged at periodic intervals in accordance with a treatment program. Again the control of the flow rate of infusate is not controlled by measuring the pressure of the infusate.
U.S. Pat. No. 4,443,218 to DeCant, Jr. et al. discloses a infusion apparatus in which the flow of infusate is controlled by the measurement of a differential pressure across a flow path through which a higher viscosity fluid is forced to flow as a result of the flow of the infusate. By responding to a measurement of the pressure drop across a flow restriction, an electric motor may be used transmit mechanical pressure to the infusate chamber to adjust the infusate flow rate. Again, the control of the flow of infusate is not related to a direct measurement of the pressure of the infusate.
PCT application WO 87/05225 to Kamen discloses a fluid dispensing system in which a infusate is transferred into a dispensing means contained in an isolated region, the amount of infusate transferred into the dispensing means determined by measuring the amount of a gas displaced from the isolated region surrounding the dispensing means. The infusate is then transferred from the dispensing means and another measurement of the gas reentering the isolated region is made. By comparing the amounts of displaced and replaced gas, it is possible to determine the amount of infusate which has been dispensed. Again, no measurement of the infusate pressure is made to determine the flow rate of infusate.
Nowhere in the prior art references is there an infusion device which overcomes many of the disadvantages of the prior art and thereby provides an infusion device which is preferably portable and includes an infusate pressure monitoring control loop adjusting infusate flow.
As well, the prior art does not disclose a means for responding to changes in infusate pressure to control the desired infusate flow rate, which is both inexpensive and in which the infusate is not contaminated.
It is therefore a primary object of the present invention to provide an infusion device which is portable and allows the administration of fluid medicaments to patients without the patient needing to be restricted to a hospital or clinic.
It is a further object of the present invention to provide an infusion device which is safe and reliable to use.
It is yet a further object of the present invention to provide an infusion device which monitors or responds to the infusate pressure and includes means to maintain the infusate pressure at a desired level.
It is another object of the present invention to provide an infusion device which is inexpensive.
Further and other objects of this invention will become apparent to those skilled in the art when considering the following summary of invention and the more detailed description of the preferred embodiments illustrated herein.